The cell membrane regulates the movement of amino acids into and out of a cell. Permeability mutants have been extremely useful in elucidating the components of transport systems and the mechanism of transport in microbial cells. The cultured plant cell is an ideal higher eukaryotic cell for a comprehensive biochemical and genetic analysis of amino acid transport because haploid cells can be cultured, permeability mutants can be selected, and whole organisms can be produced from mutant cells. For suspension cultured cells we will determine the number of systems involved in the transport of protein amino acids and for each amino acid we will determine the number of systems that transport it. This will be accomplished by kinetic analysis of amino acid uptake. For selected transport system, permeability variants will be selected. Resistance to toxic effects of an amino acid or an amino acid analogue will be initially used to identify possible permeability variants. Permeability variants will be regenerated into whole organisms where Mendelian genetic analysis can be used to identify permeability mutants. The permeability mutants thus isolated will provide the material for future investigations.